Process for treating oil-bearing formation

ABSTRACT

A process for altering the permeability of a subterranean formation comprises injecting into the subterranean formation a gelling composition which comprises a carboxylate-containing polymer, a crosslinking agent, and a liquid such as a produced brine wherein the polymer forms a gel in the formation, in the presence of the crosslinking agent. The polymer can have a molecular weight of from about 10,000 to about 1,000,000, contain about 0.01 to about 5 mole % of a carboxylate group, and be present in the gelling composition in the range of from about 100 to about 100,000 mg per liter of the composition.

FIELD OF THE INVENTION

The present invention relates to a process such as, for example, for altering permeability and correcting water coning problems of hydrocarbon-bearing subterranean formations in oil field operations.

BACKGROUND OF THE INVENTION

It is well known to those skilled in the art that gelled or crosslinked water-soluble polymers are useful in enhanced oil recovery and other oil field operations. They have been used to alter the permeability of underground formations in order to enhance the effectiveness of water flooding operations. Generally, polymers along with an appropriate crosslinking system are injected in an aqueous solution into the formation. The polymers then permeate into and gel in the regions having the highest water permeability.

Because of environmental concerns as well as cost for disposing of a produced brine which is defined as the brine co-produced with oil and gas, it is desirable to utilize the produced brine as the aqueous solution used for the polymers and appropriate crosslinking systems. Use of produced brines eliminates not only the cost associated with acquiring and pre-treating fresh water for use as the aqueous solution but also the disposal cost for the produced brine. Most produced brines are known to be hard brines, i.e., those having a divalent cation concentration greater than 1000 ppm.

Although a chromium(III) salt which is not as toxic as a chromium(VI) salt can be used as crosslinking agent, it is not an environmentally desirable compound and its use may require additional costs to assure the integrity of the injection wells to avoid contamination of ground water sources. Other multivalent metallic compounds such as compounds of zirconium, titanium, ferric or ferrous, aluminum, or combinations of any two or more thereof have been used to produce gels with synthetic water-soluble polymers or natural polymers for various oil-field operations such as, for example, water shut-off and permeability corrections for reservoirs. Usually these metallic ions crosslink gellable polymers through the interaction with the oxygen atoms of the polymer molecules. Therefore, the gellable polymers generally contain some carboxylate groups. Generally, the gellable polymers used such as, for example, polyacrylamide are of high molecular weight and contain high degrees of hydrolysis, i.e., contain 10-30 mole % carboxylate groups. However, these high molecular weight and/or high mole % carboxylate groups containing polymers gel almost instantly in the presence of the above-described multivalent metallic compounds. Such fast gelation rate renders the application of gelling compositions containing these polymers and multivalent metallic compounds not useful in many oil-field applications such as, for example, water shut-offs and permeability reductions.

Many processes have been developed to delay the gelation of gelling compositions by adding a gelation delaying agent to the gelling compositions. However, a gelation delaying agent is not inexpensive and a gelation delaying agent often adds appreciable costs to oil field operation.

Therefore, a more environmentally suitable process using a gelling composition that can form stable gels in produced brines for near-wellbore as well as in-depth treatments and that does not require a gelation delaying agent is highly desirable.

SUMMARY OF THE INVENTION

An object of the invention is to provide a process for altering the permeability of hydrocarbon-bearing formations. Another object of the invention is to provide a process for altering the permeability of hydrocarbon-bearing formations by using a gelling composition that is environmentally suitable for use in oil-field operations. A further object of the invention is to provide a process for altering the permeability of hydrocarbon-bearing formation with a gelling composition that does not require a gelation delaying agent. Still another object of the invention is to provide a process for wellbore treatment employing a gelling composition that is environmentally suitable for oil-field operations. An advantage of the invention is the invention process does not employ a gelation delaying agent, yet achieves the alteration of permeability of the formations or other oil-field applications. Other objects, features, and advantages will become more apparent as the invention is more fully disclosed hereinbelow.

According to the present invention, a process for treating hydrocarbon-bearing formation is provided which comprises injecting into the formation a gelling composition which comprises a carboxylate-containing polymer, a crosslinking agent, and a liquid wherein the gelling composition forms gels when injected into the formation.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graphic representation of gel strength of gels formed as a function of aging time at 120° F. in hard brine (a brine having 18.5% total dissolved solids or TDS; the brine was obtained from C. B. Long Unit, Stonewall County, Tex. The gels were formed from acrylamide-acrylic acid copolymers having various mole percent (%) as shown, a zirconium lactate Benchmark Research and Technology, Inc., Midland, Tex. crosslinking agent, and the brine. The concentration of the copolymer was 5,000 mg/l (ppm) and that of the crosslinking agent, measured as zirconium cation, was 250 ppm.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, a process is provided for treating a hydrocarbon-bearing formation which comprises injecting a gelling composition which comprises, or consists essentially of, or consists of, a carboxylate-containing gellable polymer, a crosslinking agent, and a liquid. Generally the gellable polymer is a water soluble polymer and is present in an aqueous solution containing a liquid. The term "liquid" used herein is interchangeable with "water" and generically refers to, unless otherwise indicated, pure water, regular tap water, a solution or suspension wherein the solution or suspension contain a variety of salts. A typical solution is a produced brine. The term "hydrocarbon" denotes any hydrocarbons which may or may not be oxygenated or substituted with appropriate substituents. The hydrocarbon may also contain minor components such as, for example, sulfur. The presently preferred hydrocarbons are crude oil and gas. The treatment includes, but is not limited to, permeability alteration, water coning correction, water shutoff, gas shutoff, and zone abandonment.

The produced brine is defined as the brine co-produced with oil or gas, or both, which generally is a hard brine, i.e., containing at least 1,000 ppm of Ca⁺², Ba⁺², Mg⁺², or Sr⁺², combinations thereof. A produced brine generally contains high salinity of from about 1 weight % to about 30% total dissolved solids. A produced brine generally is contaminated with oil or gas, or both. The gellable polymer generally gels well in produced brines having a salinity of from about 0.3% to about 27%.

The term "carboxylate-containing polymer" used herein refers to, unless otherwise indicated, a polymer that contains at least one free carboxylic group or a carboxylate group in which the proton of the carboxylic acid is substituted with an ammonium radical, an alkali metal, an alkaline earth metal, or combinations of any two or more thereof.

According to the present invention, the molecular weight of the carboxylate-containing polymers is generally at least about 10,000 and less than about 1,000,000, preferably less than about 800,000, more preferably less than about 700,000, still more preferably less than about 600,000, and most preferably less than 500,000. The mole percent % of the carboxylate group is generally in the range of from about 0.01 to less than about 5, preferably about 0.1 to less than about 2, more preferably about 0.1 to less than about 1, even more preferably about 0.1 less than about 0.5, even more preferably less than about 0.4, and most preferably about 0.2 to about 0.3 mole %.

According to the present invention, the gelation rate is defined as the rate at which gel particles are formed. At the onset of gelation these particles are small enough that the gelling solution still flows, but these particles can be detected from apparent flow characterization caused by the apparent viscosity change. The small particles grow to larger granules with time and become strong enough to hold fluids within their structures which restrict the free flowing characterizing of the gelling solution and thus, develop tongue length. The gelation rate is generally longer than about 1 hour, preferably longer than about 2 hours, more preferably longer than about 3 hours, even more preferably longer than about 4 hours, and most preferably longer than 10 hours. Generally, no appreciable gel strength, as defined in Example I, is observed until a tongue length can be measured.

Carboxylate-containing polymers suitable for use in this invention are those capable of gelling in the presence a crosslinking agent such as, for example, a multivalent metallic compound. Polymers suitable for use in this invention, i.e., those capable of gelling in the presence of a crosslinking agent, include, but are not limited to, biopolysaccharides, cellulose ethers, and acrylamide-containing polymers.

Suitable cellulose ethers are disclosed in U.S. Pat. No. 3,727,688 (herein incorporated by reference). Particularly preferred cellulose ethers include carboxymethylhydroxyethyl cellulose (CMHEC) and carboxymethyl cellulose (CMC) for their ready availability.

Suitable biopolysaccharides are disclosed in U.S. Pat. No. 4,068,714 (herein incorporated by reference). Particularly preferred is polysaccharide B-1459 and xanthan gums which are biopolysaccharides produced by the action of Xanthomonas campestris bacteria. This biopolysaccharide is commercially available in various grades under the tradename "KELZAN®" (Kelco Company, Los Angeles, Calif.) and "FLOCON " 4800 (Pfizer, Groton, Conn.) and they are readily available.

Suitable acrylamide-containing polymers which also contain pendant carboxylate groups are disclosed in U.S. Pat. No. 3,749,172 (herein incorporated by reference). Particularly preferred are the so-called partially hydrolyzed polyacrylamides possessing pendant carboxylate groups through which crosslinking can take place. Thermally stable carboxylate-containing polymers of acrylamide, such as copolymers of N-vinyl-2-pyrrolidone and acrylamide, terpolymers of sodium-2-acrylamido-2-methylpropanesulfonate, acrylamide and N-vinyl-2-pyrrolidone, and copolymers of sodium-2-acrylamido-2-methylpropanesulfonate and acrylamide, are particularly preferred for applications in high salinity environments at elevated temperatures for stability. Selected carboxylate-containing terpolymers also are useful in the present process, such as terpolymers derived from acrylamide and N-vinyl-2-pyrrolidone comonomers with lesser amounts of termonomers such as vinyl acetate, vinylpyridine, styrene, methyl methacrylate, and other polymers containing acrylate groups.

Generally, suitable polymers contain some carboxylate group if the polymers are used to crosslink with multivalent cations such as Zr, Ti, Fe, and Al cations. In the absence of the carboxylate group, the polymers can also be used to crosslink with organic crosslinkers such as, for example, phenol and formaldehyde, or precursors thereof, or furfuryl alcohol and formaldehyde, or an aminobenzoic acid and formaldehyde. Precursors of formaldehyde such as, for example, hexamethylenetetramine can be, and are more preferably, used in place of formaldehyde.

Other miscellaneous polymers suitable for use in the present invention include partially hydrolyzed polyacrylonitriles, copolymers of acrylate and styrene sulfonate, or combinations of any two or more thereof.

The presently preferred carboxylate-containing polymers are CMHEC, CMC, xanthan gum, and the acrylamide-containing polymers, particularly the partially hydrolyzed polyacrylamides, polymers containing acrylamide, ammonium or alkali metal salts of acrylic acid, and polymers containing ammonium or alkali metal salts of acrylic acid, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methylpropanesulfonate. The ammonium or alkali metal salts of acrylic acid are herein referred to as acrylate, as in the claims.

Any crosslinking agents such as, for example, a multivalent metallic compound that are capable of crosslinking the gellable carboxylate-containing polymer in the hydrocarbon-bearing formations can be used in the process of the present invention. The presently preferred multivalent metal compound is a metal compound selected from the group consisting of a complexed zirconium compound, a complexed titanium compound, and mixtures thereof. Examples of suitable multivalent metallic compounds include, but are not limited to, zirconium citrate, zirconium complex of hydroxyethyl glycine, ammonium zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate, zirconium neodecanoate, zirconium acetylacetonate, tetrakis(triethanolamine)zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium lactate, titanium acetylacetonate, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate, chromium citrate, chromium acetate, chromium propionate, and combinations thereof. The presently most preferred crosslinking agent is zirconium lactate, zirconium citrate, tetrakis(triethanolamine)zirconate, or zirconium complex of hydroxyethyl glycine, or combinations thereof. These compounds are commercially available.

According to the present invention, the crosslinking agent can also contain a complexing ligand if necessary to further delay the rate of gelation. Preferably, however, the crosslinking agent does not contain such complexing agent. The complexing ligand useful for the present invention to retard the rate of gelation is generally a carboxylic acid containing one or more hydroxyl groups and salts thereof. The complexing ligand can also be an amine that has more than one functional group and contains one or more hydroxyl groups and that can chelate the zirconium or titanium moiety of the zirconium or titanium compounds described above. Examples of suitable complexing ligands include, but are not limited to, hydroxyethyl glycine, lactic acid, ammonium lactate, sodium lactate, potassium lactate, citric acid, ammonium, potassium or sodium citrate, isocitric acid, ammonium, potassium or sodium isocitrate, malic acid, ammonium, potassium or sodium malate, tartaric acid, ammonium, potassium or sodium tartrate, triethanolamine, malonic acid, ammonium, potassium or sodium malonate, and mixtures thereof. The presently preferred complexing ligands are citric acid, lactic acid, tartaric acid and salts thereof, triethanolamine, and hydroxyethyl glycine because of their ready availability and low cost.

The concentration or amount of the carboxylate-containing polymer in the gelling composition can range widely and be as suitable and convenient for the various polymers, and for the degree of gelation needed for particular reservoirs. Generally, the concentration of polymer in an aqueous solution is made up to a convenient strength of about 100 to 100,000 mg/l (ppm), preferably about 200 to 70,000 ppm, and most preferably 1,000 to 50,000 ppm.

Any suitable procedures for preparing the aqueous admixtures of the gellable polymer can be used. Some of the polymers can require particular mixing conditions, such as slow addition of finely powdered polymer into a vortex of stirred brine, alcohol prewetting, protection from air (oxygen), preparation of stock solutions from fresh rather than salt water, as is known for such polymers.

The concentration of crosslinking agent used in the present invention depends largely on the concentrations of polymer in the composition. Lower concentrations of polymer, e.g., require lower concentrations of the crosslinking agent. Further, it has been found that for a given concentration of polymer, increasing the concentration of crosslinking agent generally substantially increases the rate of gelation. The concentration of crosslinking agent in the injected slug varies generally over the broad range of about 1 mg/l (ppm) to about 5,000 ppm, preferably over the range of about 1 ppm to about 3,000 ppm, and most preferably 1 ppm to 2,000 ppm.

The concentration of the complexing ligand, if present, in the composition also depends on the concentrations of the water-soluble polymer in the composition and on the desired rate of gelation. Generally, the lower the concentration of the complexing ligand is, the faster the gelation rate is.

The use of gelled polymers to alter the water permeability of underground formations is well known to those skilled in the art. Generally, an aqueous solution containing the polymer and a crosslinker is pumped into the formation so that the solution can enter into the more water swept portions of the formation and alter water permeability by gelling therein.

According to the process of the present invention, an aqueous gelling composition comprising a crosslinking agent and a gellable carboxylate-containing polymer is injected into an injection or production well. The definition and scope of the crosslinking agent and polymer are the same as those described above. The amount of the aqueous gelling composition injected can vary widely depending on the treatment volume injected. The amount of the gellable polymer injected is also dependent on the gel strength desired, same as that described for the crosslinking agent.

The nature of the underground formation treated is not critical to the practice of the present invention. The described gelling composition can be injected into a formation having a temperature range of from about 70° F. to about 300° F. when the polymer used is a gelling copolymer suitable for the brine used at the reservoir temperature or temperatures in the range of from about 70° F. to about 300° F. for partially hydrolyzed polyacrylamide, xanthan gum, CMC, or CMHEC, preferably about 80° F. to about 180° F., and most preferably 80° F. to 170° F. for best results. Any means known to one skilled in the art can be used for injecting the gelling composition and polymer solution.

Examples provided hereinbelow are intended to assist one skilled in the art to further understand the invention and should not be considered limitative.

EXAMPLE I

The purpose of this example is to illustrate the gelation of a composition comprising a water-soluble polymer, a crosslinking agent, and a brine, and to use this example as a control.

Polyacrylamide solutions (0.5%) were prepared by mixing sufficient amount of the polymer in a synthetic brine having 1.1%, total dissolved solids (TDS; 1% NaCl and 0.1% CaCl₂), 11% TDS (10% NaCl and 1% CaCl₂), and 22% TDS (20% NaCl₂ and 2% CaCl₂). Then 20 ml samples of each polymer solution were placed in three vials. Each vial was then charged with tetrakis(triethanolamine)zirconate. The vials were placed upright in test tube racks and then placed in ovens heated to and held at 120° F. Periodically, the ampules were removed from the oven and the mechanical strength of the gels was determined.

As crosslinking developed, small microgels of granules began to appear, i.e., a very slight gel formed. Continued growth of the microgels to globule occurred next, referred to as slight gel. Larger gel masses next appeared, referred to as partial gel, followed by the development of stronger gels with measurable tongue lengths. The tongue lengths were measured by placing each vial horizontally allowing the gelling composition to flow to its equilibrium position and then measuring the length of the tongue formed. As gelation progressed with time, stronger gels and shorter tongue lengths were developed. The gel strength is expressed mathematically as

    Percent Gel Strength=(AL-TL)×100/AL

where AL equals ampule length (in centimeters), and TL equals the tongue length of the gel measured in centimeters from the point at which the gel contacts the entire circumference of the tube to the farthest point to which the gel has spread. Thus the strongest gels would have a gel strength of 100% and the weakest gels would have a gel strength of 0. The gel strength results are shown in Table I.

                  TABLE I                                                          ______________________________________                                         Gelation of Polyacrylamide.sup.a in Brines with                                250 ppm Zirconium ("Zirtech TE".sup.b) at 120° F.                       In 1.1% Brine                                                                              In 11% Brine  In 22% Brine                                         Aging  Gel      Aging    Gel    Aging  Gel                                     Time   Strength Time     Strength                                                                              Time   Strength                                (days) (%)      (days)   (%)    (days) (%)                                     ______________________________________                                         0.06   0.00     0.07     64.4   0.06   84.0                                    0.15   64.9     0.17     70.7   0.16   84.0                                    0.81   71.6     0.84     77.3   0.84   86.7                                    2.90   78.7     3.90     80.4   3.90   87.1                                    4.90   81.3     5.90     83.6   5.80   87.6                                    7.00   81.3     7.90     84.4   7.80   88.4                                    11.30  83.6     14.90    85.3   14.90  90.7                                    18.20  84.4     22.00    86.2   21.90  88.9                                    25.20  84.0     29.00    87.1   28.90  91.1                                    32.00  86.2     36.00    87.1   36.00  91.1                                    39.00  86.2     43.00    85.8   43.00  91.6                                    46.00  87.6     77.00    87.1   70.00  90.7                                    53.00  88.4     152.00   85.8   146.00 77.8                                    87.00  88.4     246.00   82.7   193.00 77.8                                    162.00 88.4                                                                    256.00 88.4                                                                    ______________________________________                                          .sup.a Polymer used was "Polydia 1041" (% hydrolysis = 3-6; inherent           viscosity = 18 dL/g) obtained from Nilto Chemical Industry Co., Tokyo,         Japan.                                                                         .sup.b "Zirtech TE" is a triethanolamine complex of zirconium obtained         from Benchmark Research and Technology, Inc., Midland Texas              

The results shown in Table I indicate that increasing the salinity of the brines from 1.1% to 22% significantly increased the gelation rate. For example, aging for 1.4 hours (0.06 day), the gel strength in 1.1% brine was 0.0 The gel strength in 22% brine, for same aging period, increased to 84%. However, upon prolonged incubation, the gels formed in lower salinity brine appear to be stronger than those formed in higher salinity brines. For example, upon aging for 256 days in 1.1% brine, the gel strength was 88.4%. On the other hand, upon aging for 193 days in 22% brine, the gel strength was only 77.8%.

EXAMPLE II

This example illustrates the gelation of water-soluble polymer with a complexed zirconium compound in a produced brine.

The runs were carried out the same as those described in Example I with the exception that the brine used as a produced brine obtained from Tank Battery 41 of North Burbank Unit Oil Field, Shidler, Okla. The produced brine has a TDS of 5%. Gel strength of the gels aged at 120° F., 150° F. and 175° F. is shown in Table II.

                  TABLE II                                                         ______________________________________                                         Gelation of Polyacrylamide in a Produced Brine with                            "Zirtech TE".sup.a (250 ppm Zr) at 120° F., 150° F. and          175° F.                                                                             Gel Strength (%)                                                   Aging Time (days)                                                                            120° F.                                                                            150° F.                                                                         175° F.                                ______________________________________                                         0.06          0.0        65.8    84.9                                          0.17          0.0        74.7    92.4                                          0.83          67.6       83.6    94.2                                          1.20          72.4       85.3    95.1                                          1.90          74.2       87.1    96.0                                          2.80          77.8       88.4    95.6                                          7.80          80.4       89.8    96.4                                          20.00         83.6       91.6    96.9                                          26.90         84.9       92.4    97.3                                          34.00         84.9       92.0    96.9                                          49.00         86.2       93.8    91.1                                          66.00         87.6       93.3    86.2                                          97.00         89.3       93.8    Syneresis                                     125.00        88.4       93.8    Syneresis                                     ______________________________________                                          .sup.a See footnote b, Table I.                                          

Table II shows that the lower the aging temperature, the slower the gelation rate. For instance, no gel was observed at 120° F. until after the gelling composition had been aged for more than 4.1 hours (0.17 day). It gelled, however, within 1.4 hours of aging at 150° F. as well as at 175° F. Table II further indicates that the gelation rate at higher temperature, i.e. 150° F. to 175° F., needed to be delayed so that the components of the gelling composition can be simultaneously injected into an oil well.

EXAMPLE III

This example demonstrates that lactic acid can be used in a gelling composition comprising polyacrylamide and a complexed zirconium compound, in a produced brine to delay the gelation rate.

The runs were carried out the same as those described in Example II except that zirconium lactate was used as the crosslinking agent and lactic acid was used as a complexing ligand to delay gelation. Results presented in Table III indicate that lactic acid was an effective complexing ligand for delaying the gelation of a gelling composition.

                  TABLE III                                                        ______________________________________                                         Gelation of Polyacrylamide in a Produced Brine with                            283 ppm Zr (Zirconium Lactate, "Zirtech LA".sup.a) at 120° F.           0 ppm Lactic Acid 1650 ppm Lactic Acid                                         Aging     Gel         Aging      Gel                                           Time (days)                                                                              Strength (%)                                                                               Time (days)                                                                               Strength (%)                                  ______________________________________                                         0.04      0.0         0.04       0.0                                           0.14      72.0        0.08       0.0                                           0.22      74.7        0.16       0.0                                           0.89      78.2        0.27       0.0                                           5.90      82.2        0.88       0.0                                           10.20     82.2        1.10       0.0                                           13.20     82.7        2.20       0.0                                           20.90     78.7        3.20       0.0                                           38.00     83.1        6.20       0.0                                           59.00     82.7        13.90      0.0                                           104.00    84.4        31.00      69.8                                          240.00    83.1        52.00      82.2                                                                97.00      89.3                                                                233.00     95.6                                          ______________________________________                                          .sup.a "Zirtech LA" is a zirconium lactate obtained from Benchmark             Research and Technology, Inc., Midland, Texas.                           

EXAMPLE IV

This example illustrates the relationship of gelation of a gelling composition and the mole % of carboxylate group of a gellable polymer used in the gelling composition.

The runs were carried out the same as those described in Example I with the exception that the polymers used had different mole percent of carboxylate group, the produced brine used contained 18.5% TDS, and zirconium lactate was used as crosslinking agent. The results are shown in FIG. 1.

As shown in FIG. 1, a gelling composition containing 0.5 mole % or higher carboxylate gelled in less than 2 hours and the gel strength reached about 75% in about 5 hours when the zirconium ion concentration was 250 mg/l (ppm). FIG. 1 also shows that essentially no gels were formed if the gelling composition contained 0 mole % or 0.1 mole % carboxylate group.

EXAMPLE V

This example illustrates that a gelling composition containing a high molecular weight polyacrylamide having high degree of hydrolysis forms gels in less than 1.2 hours.

The runs were carried out the same as those described in Example I with the exception that a different polyacrylamide, various concentrations of zirconium lactate was used as crosslinking agent, and a produced brine FKWO (obtained from the South Cowden Unit, Ector County, Tex.; 7.86% TDS) was used in gelling composition shown in Table IV.

Table IV shows that, with as low as 250 ppm of zirconium lactate, gels were formed in 1.2 hours.

                  TABLE IV                                                         ______________________________________                                         Bulk Gel Test With "OFXC-1163".sup.a and "Zirtech LA 110".sup.b                in Aerated FKWO Water at 120° F.                                        Polymer                                                                               Zr      0      1.2   2.0  4.4  5.8  23.2 15.0                           Concn. Concn.  hr     hr    hr   hr   hr   hr   d                              ppm    ppm     Gel Strength (%)                                                ______________________________________                                         5000   250     NG     S-PG  PG   PG   PG   PG   PG                             5000   500     NG     S-PG  PG   63.6 65.8 74.7 81.3                           5000   750     NG     PG    PG   PG   63.1 78.2 86.7                           5000   1000    NG     S-PG  PG   PG   PG   75.1 89.8                           5000   1500    NG     S-PG  PG   PG   PG   68.4 87.6                           5000   2000    T      S-PG  S-   PG   PG   61.8 82.7                                                       PG                                                 ______________________________________                                          NG = No gel, T = Thick, VT = Very thick, SG = Slight gel, PG = Partial         gel, S-PG = Slight to partial gel.                                             .sup.a "OFXC1163" is a partially hydrolyzed polyacrylamide, having a           molecular weight of about (10-15) × 10.sup.6 and 5-7 mole %              carboxylate group, obtained from American Cyanamid Company, West Paterson      New Jersey.                                                                    .sup.b See footnote a, Table III.                                        

EXAMPLE VI

This example demonstrates that the higher degree of hydrolysis is, i.e., higher mole % content of carboxylate of the polymer, the faster the gelation rate.

The runs were carried out the same as those described in Example V with the exception that a different polyacrylamide and a different produced brine shown in Table V were used. The results in Table V show that in less than 1.5 hours, the gelling composition containing as low as 250 ppm of zirconium formed strong gels.

                  TABLE V                                                          ______________________________________                                         Bulk Gel Test With Tiorco "Uniperm 420".sup.a and                              "Zirtech LA 110".sup.b in Aerated FKWO Water at 120° F.                 Polymer                                                                               Zr       0       1.4  2.9   4.4  20.8  16.9                             Concn. Concn.   hr      hr   hr    hr   hr    d                                ppm    ppm      Gel Strength (%)                                               ______________________________________                                         5000   250      T       76.9 79.1  80.0 83.1  85.3                             5000   500      T       84.0 86.7  88.4 92.4  93.8                             5000   750      T       83.6 88.0  90.7 95.1  95.6                             5000   1000     T       81.8 87.1  90.2 96.0  97.3                             5000   1500     T       76.0 85.3  88.4 96.4  98.2                             5000   2000     T       71.1 83.1  85.8 95.1  97.8                             ______________________________________                                          T = Thick                                                                      .sup.a Tiorco "Uniperm 420" is a partially hydrolyzed polyacrylamide,          having a molecular weight of about (13-14) × 10.sup.6 and about 18       mole % carboxylate group, obtained from TIORCO, Inc., Englewood, Colorado      .sup.b See footnote a, Table III.                                        

EXAMPLE VII

This example illustrates a gelling composition containing a different produced brine also has very fast gelation rate,

The runs were carried out the same as those described in Example V except that a C.B. Long brine (obtained from C.B. Long Unit, Stonewall County, Tex.; 18.5% TDS) was used in place of FKWO brine. The results shown in Table VI indicate that the gelation rate of the gelling composition were similar to the results shown in Table V.

                  TABLE VI                                                         ______________________________________                                         Bulk Gel Test With "OFXC-1163".sup.a "Zirtech LA 110".sup.b                    in C.B. Long Brine at 120° F.                                           Polymer                                                                               Zr      0      1.0  2.0   4.1   18.2  27.8                              Concn. Concn.  hr     hr   hr    hr    hr    d                                 ppm    ppm     Gel Strength (%)                                                ______________________________________                                         5000   250     VT     84.4 93.3  93.3  91.6  93.8                              5000   500     VT     93.8 92.9  94.7  94.7  96.4                              5000   750     VT     75.1 76.4  80.9  85.8  90.2                              5000   1000    VT     65.3 71.6  77.3  80.0  83.1                              5000   1500    T      PG   62.7  76.0  76.0  86.7                              ______________________________________                                          VT = Very thick, T = Thick, PG = Partial gel.                                  .sup.a See footnote a, Table IV.                                               .sup.b See footnote a, Table III.                                        

EXAMPLE VIII

This example demonstrates that decreasing the mole % of carboxylate group in polyacrylamide significantly lowers the gelation rate of a gelling composition which does not contain a gelation delaying agent.

The runs were carried out the same as described in Example VII with the exception that a polyacrylamide having less than 1 mole % of carboxylate group was used. The results shown in Table VII demonstrate that strong gels did not form until after being aged for over 47 days.

                                      TABLE VII                                    __________________________________________________________________________     Bulk Gel Test with "Cytec 4500".sup.a and "Zirtech LA 110".sup.b               in C.B. Long Brine at 12o° F.                                           Polymer Concn.                                                                          Zr Concn.                                                                            0 hr                                                                              1 hr                                                                              2.0 hr                                                                             3.0 hr                                                                             4.2 hr                                                                             22.5 hr                                                                            47 d                                                                               71 d                                  ppm      ppm   Gel Strength (%)                                                __________________________________________________________________________     5000     250   T  VT SG  SG  SG  SG  PG  69.8                                  5000     500   T  T  VT  VT  SG  SG  PG  75.1                                  5000     750   T  T  T   T   VT  VT  PG  62.2                                  5000     1000  T  T  T   T   VT  VT  S-PG                                                                               PG                                    __________________________________________________________________________      T--Thick, VT--Very thick, SG = Slight gel, PG = Partial gel, S-PG = Sligh      partial gel.                                                                   .sup.a "Cytec 4500" is a partially hydrolyzed polyacrylamide, having a         molecular weight of about 15 × 10.sup.6 and less than 1 mole %           carboxylate group, obtained from American Cyanamid Company, West Paterson      New Jersey.                                                                    .sup.b See footnote a, Table III.                                        

EXAMPLE IX

This example shows that a gelling composition containing a low molecular weight polyacrylamide has a significantly lower gelation rate as compared to a gelling composition containing a high molecular weight polyacrylamide.

The runs were carried out the same as those described in Example VII except that a lower molecular weight polyacrylamide was used in the gelling composition. As shown in Table VIII, a composition containing a polyacrylamide having a molecular weight of about 300,000 had significantly lower gelation rate as compared to the results of Table VI. For example, with 250 ppm of zirconium in the composition, no strong gels were formed until the composition was aged for over 25 days.

                  TABLE VIII                                                       ______________________________________                                         Bulk Gel Test With Allied "Colloids 254S".sup.a                                Zirtech LA 110.sup.b in C.B. Long Brine at 120° F.                      Polymer                                                                              Zr      0      1    2.2  3.1  5.2   24.7  70                             Concn.                                                                               Concn.  hr     hr   hr   hr   hr    hr    d                              ppm   ppm     Gel Strength (%)                                                 ______________________________________                                         20000 250     NG     NG   T    T    VT    S-PG  93.8                           20000 500     NG     T    T    VT   S-PG  PG    97.3                           20000 750     NG     T    T    VT   SG    PG    97.8                           20000 1000    NG     T    T    T    T     S-PG  97.8                           20000 1500    NG     T    T    T    T     T     97.8                           ______________________________________                                          NG = No gel, T = Thick, VT = Very thick, VSG = Very slight gel, SG =           Slight gel, PG = Partial gel, S-P = Slight to partial gel.                     .sup.a Allied "Colloids 254S" is a partially hydrolyzed polyacrylamide,        having a molecular weight of about 300,000 and about 4-5 mole %                carboxylate group, obtained from Allied Colloids, Inc., Sulfolk, Virginia      .sup.b See footnote a, Table III.                                        

EXAMPLE X

This example illustrates a synergistic effect of employing a carboxylate-containing polymer which has both a low molecular weight and a low mole % of carboxylate group.

The runs were carried out the same as those described in Example V except that a polyacrylamide having a molecular weight of less than 300,000 and containing about 0.3 mole % carboxylate group, and a produced brine obtained from Point Arguello, Santa Barbara, Calif. (TDS=2.63%) were used. The results shown in Table IX below demonstrate that, at 250 ppm of zirconium, no gels were formed after the composition was aged for 24 days.

                  TABLE IX                                                         ______________________________________                                         Bulk Gel Test With Allied "Colloids DP-6193".sup.a and                         "Zirtech LA110".sup.b in Point Arguello Brine.sup.c                            Polymer                                                                               Zr       0      1.1  2.7  6.0  22.5 2    24                             Concn. Concn.   hr     hr   hr   hr   hr   d    d                              ppm    ppm      Tongue Length (TL), cm                                         ______________________________________                                         27500  250      NG     NG   NG   NG   NG   NG   NG                             27500  500      NG     NG   NG   NG   NG   NG   NG                             27500  750      NG     NG   NG   NG   NG   NG   NG                             27500  1000     NG     NG   NG   NG   NG   T                                   ______________________________________                                          NG--No gel, T = Thick, VT = Very thick, VSG = Very slight gel, SG = Sligh      gel, PG = Partial gel.                                                         .sup.a "DP96193" is a polyacrylamide obtained from Allied Colloids, Inc.,      Sulfolk, Virginia which had a carboxylate content of about 0.3 mole % and      a molecular weight of less than 300,000.                                       .sup.b See Table III, footnote a.                                              .sup.c Contained about 2.63% TDS and was obtained from Point Arguello,         Santa Barbara, California.                                               

The results shown in the above examples clearly demonstrate that the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While modifications may be made by those skilled in the art, such modifications are encompassed within the spirit of the present invention as defined by the specification and the claims. 

That which is claimed is:
 1. A process comprising injecting a gelling composition into a subterranean formation wherein said composition comprises a carboxylate-containing polymer, a crosslinking agent and a liquid wherein said polymer forms gels, in the presence of said crosslinking agent, when injected into a subterranean formation; said crosslinking agent is a multivalent metallic compound whose metal is selected from the group consisting of Zr, Ti, Fe, Al, and combinations of any two or more thereof, and does not contain a gelation-delaying agent; and said polymer has an effective molecular weight sufficient to effect the delaying of gelation of said composition.
 2. A process according to claim 1 wherein said crosslinking agent is selected from the group consisting of zirconium complex of hydroxyethyl glycine, ammonium zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate, zirconium decanoate, zirconium acetylacetonate, tetrakis(triethanolamine)zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium citrate, zirconium lactate, titanium acetylacetonate, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate, and combinations of any two or more thereof.
 3. A process according to claim 2 wherein said crosslinking agent is zirconium lactate, zirconium citrate, tetrakis(triethanolamine)zirconate, zirconium complex of hydroxyethyl glycine, and combinations thereof.
 4. A process according to claim 1 wherein said liquid is a produced brine.
 5. A process according to claim 1 wherein said polymer is selected from the group consisting of biopolysaccharides, cellulose ethers, acrylamide-containing polymers, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacylonitrile, and combinations of any two or more thereof.
 6. A process according to claim 5 wherein said polymer is selected from the group consisting of partially hydrolyzed polyacrylamide, copolymers of acrylamide and N-vinyl-2-pyrrolidone, copolymers of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate, terpolymers of acrylamide, N-vinyl-2-pyrrolidone, and 2-acrylamido-2-methylpropane sulfonate, copolymers of acrylate and styrene sulfonate, carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose, and combinations of any two or more thereof.
 7. A process according to claim 5 wherein said polymer is selected from the group consisting of partially hydrolyzed polyacrylamide, carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and combinations of any two or more thereof.
 8. A process according to claim 1 wherein said polymer contains a carboxylate group in the range of from about 0.01 to about 5 mole %.
 9. A process according to claim 1 wherein said polymer contains a carboxylate group in the range of from 0.1 to 2 mole %.
 10. A process according to claim 5 wherein said polymer contains a carboxylate group in the range of from about 0.1 to about 0.5 mole %.
 11. A process according to claim 5 wherein said polymer contains a carboxylate group in the range of from 0.1 to 0.4 mole %.
 12. A process according to claim 11 wherein said crosslinking agent is zirconium lactate, zirconium citrate, tetrakis(triethanolamine)zirconate, zirconium complex of hydroxyethyl glycine, and combinations thereof.
 13. A process according to claim 1 wherein the molecular weight of said polymer is in the range of from about 10,000 to about 1,000,000.
 14. A process according to claim 1 wherein the molecular weight of said polymer is in the range of from 10,000 to 500,000.
 15. A process according to claim 1 wherein said polymer is present in said composition in the range of from about 100 to about 100,000 mg/l.
 16. A process according to claim 1 wherein said polymer is present in said composition in the range of from 1,000 to 50,000 mg/l.
 17. A process according to claim 1 wherein said polymer contains a carboxylate group in the range of from about 0.1 to about 0.5 mole % and the molecular weight of said polymer is in the range of from about 10,000 to about 700,000.
 18. A process according to claim 1 wherein said polymer contains a carboxylate group in the range of from 0.1 to 0.4 mole % and the molecular weight of said polymer is in the range of from 10,000 to 500,000.
 19. A process comprising injecting a gelling composition into a subterranean formation wherein said gelling composition comprises:a carboxylate-containing polymer having a molecular weight in the range of from about 10,000 to about 700,000 and containing a carboxylate group in the range of from about 0.1 to about 1 mole % wherein said polymer is selected from the group consisting of biopolysaccharides, cellulose ethers, acrylamide-containing polymers, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, and combinations of any two or more thereof; a crosslinking agent selected from the group consisting of zirconium complex of hydroxyethyl glycine, ammonium zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate, zirconium decanoate, zirconium acetylacetonate, tetrakis(triethanolamine)zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium citrate, zirconium lactate, titanium acetylacetonate, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate, and combinations of any two or more thereof; a produced brine; said composition does not comprise a gelation delaying agent; and said polymer is present in said composition in the range of from about 100 to about 100,000 mg/l and said crosslinking agent is present in said composition in the range of from about 1 to about 5,000 mg/l.
 20. A process according to claim 19 wherein said polymer is selected from the group consisting of partially hydrolyzed polyacrylamide, carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose, and combination of any two or more thereof; said polymer has a molecular weight in the range of from 10,000 to 500,000, contains a carboxylate group in the range of from 0.1 to 0.4 mole %, and is present in said composition in the range of from 1,000 to 50,000 mg/l; and said crosslinking agent is selected from the group consisting of zirconium complex of hydroxyethyl glycine, tetrakis(triethanolamine)zirconate, zirconium citrate, zirconium lactate, and combinations thereof and is present in said composition in the range of from 1 to 2,000 mg/l.
 21. A process according to claim 20 wherein said polymer is a partially hydrolyzed polyacrylamide and said crosslinking agent is zirconium lactate.
 22. A process comprising injecting a composition into a subterranean formation wherein said composition consisting essentially of a partially hydrolyzed polyacrylamide having a molecular weight of about 300,000, has a carboxylate group in the range of from 0.1 to 0.4 mole %, and is present in said composition in the range of from 1,000 to 50,000 mg/l zirconium lactate which is present in said composition in the range of from 1 to 2,000 mg/l and a produced brine which makes up the rest of said composition. 